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ADP3804JRU

High Frequency Switch Mode Li-Ion Battery Charger

Analog Devices 

ADP3804

VIN

C14

2.2µF

Q1

IRF7807

R13

10Ω

C15 +

220µ F

C9

0.1µF

VCC BST DRVH SW

L1

Q2

22µ H

C16

+

IRF7807D2 220µF

DRVL PGND

CS+

RCS

50mΩ

R3

249Ω

C13

22nF

CS-

RSS1

10mΩ

R4

R1

249Ω 10Ω

C1

470nF

SYS+ SYS-

SYSTEM

DC/DC

R2

10Ω

C2

470nF

ISYS

BATTERY

12.6V

BOOSTED

SYNCHRONOUS

DRIVER

+

AMP

1

AMP+

2

BSTREG

7.0V

C10

0.1µF

VREF + VREG

UVLO

BIAS

VREF

gm1

2.5V

LIMIT

*R11

412k

0.1%

ISET

SD

LOGIC

CONTROL

RY CCCV

A **R7

IN L 100k

ADP3804

LIM ICA AGND

OSCILLATOR

gm2

REG

6.0V

REF

2.5V

SYNC

C7

200pF

CT

C6

200pF

COMP

C8

1µF R8

56Ω

VREF

ADJ

RE N C17

P H 100nF

C A * ADP3804-12.6: R11 = SHORT, R12 = OPEN

TE DAT ** R7, OPEN IF CCCV FUNCTION IS NOT USED

Figure 1. Typical Application

ADP3804-12.6

SD

BAT

ADP3804-12.5

R5

6.81kΩ

R6

7.5kΩ

*R12

102k

0.1%

THEORY OF OPERATION

The ADP3804 combines a boosted synchronous switching

driver with programmable current control and accurate final

battery voltage control in a Constant Current, Constant Volt-

age (CCCV) Li-Ion battery charger. High accuracy voltage

control is needed to safely charge Li-Ion batteries, which are

typically specified at 4.2 V ± 1% per cell. For a typical note-

book computer battery pack, three cells are in series giving a

total voltage of 12.6 V. The ADP3804 is available in three

versions, a fixed 12.525 V output, a fixed 12.6 V output and an

adjustable output. The adjustable output is useful for charging

batteries with slightly different chemistry that result in a final

battery voltage slightly higher or lower than 4.2 V/ cell.

Another requirement for safely charging Li-Ion batteries is

accurate control of the charge current. The actual charge cur-

rent depends on the number of cells in parallel within the bat-

tery pack. Typically this is in the range of 2 A to 3 A. The

ADP3804 provides flexibility in programming the charge cur-

rent over a wide range. An external resistor is used to sense the

charge current and this voltage is compared to a DC input

voltage. This programmability allows the current to be changed

during charging. For example, the charge current can be re-

duced for trickle charging.

The synchronous driver provides high efficiency when charging

at high currents. Efficiency is important mainly to reduce the

amount of heat generated in the charger, but also to stay within

the power limits of the AC adapter. With the addition of a

boosted high side driver, the ADP3804 drives two external

power NMOS transistors for a simple, lower cost power stage.

The ADP3804 also provides an uncommitted current sense

amplifier. This amplifier provides an analog output pin for

monitoring the current through an external sense resistor. The

amplifier can be used anywhere in the system that high side

current sensing is needed.

Charge Current Control

AMP1 in Figure 1 has a differential input to amplify the voltage

drop across an external sense resistor RCS. The input common

mode range is from ground to VCC allowing current control in

short circuit and low drop-out conditions. The gain of AMP1 is

internally set to 25 V/V for low voltage drop across the sense

resistor. During CC mode, gm1 forces the voltage at the output

of AMP1 to be equal to the external voltage at the ISET pin.

By choosing RCS and VISET appropriately, a wide range of

charge currents can be programmed:

ICHARGE

=

VISET

25×RCS

(1)

REV. PrI

–5–

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